Heavy metal variation and characterization change of dissolved organic matter (DOM) obtained from composting or vermicomposting pig manure amended with maize straw.

A mixture of pig manure and maize straw was vermicomposted with Eisenia fetida or naturally composted for 60 days; basic parameters, heavy metal variation, dissolved organic matter (DOM) content, and its characterization were determined, aiming to explore different dynamics of DOM characterization and heavy metal variation during composting or vermicomposting. The results showed that vermicomposting led to higher pH, TC, and available P but lower EC, TN, available N, and available K in the substrate residues compared with natural composting; the total or available Cu/Zn content in the substrate residues similarly increased after composting or vermicomposting, but Cu was easily enriched in earthworm bodies and its intestinal vermicompost while vermicomposting enhanced the formation of dissolved Zn in DOM; moreover, much more fulvic and humic acid-like materials and much greater aromaticity were exhibited in DOM obtained from vermicomposting residues compared with DOM from composting residues, which may contribute to the variations of Cu/Zn enrichment in earthworms and its migration to the vermicomposting residues or its DOM.